The role of illicit and medicinal drugs in motor vehicle crashes is widely assumed to be substantial, but no study has yet determined even the prevalence of the major psychoactive drugs among the general driving population. Thus, it has not been possible to assess their relative risk of becoming involved in crashes in which drugs played a part. The proposed project (Phase 1) is designed to address these gaps by (1) determining the prevalence and quantity of such drugs in the crash-injured driving population, sampled at hospitals and medical examiner facilities, and (2) estimating the relative risk of crashing by obtaining data on the prevalence and quantity of drugs among drug-positive vs. drug-negative crash-involved drivers. Blood samples will provide the basis for determining drug and alcohol quantities among the seriously and fatally injured drivers. The proposed project site is San Diego County, where saliva samples will be collected from injured drivers to determine both the presence and quantity of selected drugs. To assess the validity and sensitivity of the saliva assays, they will be compared to the blood assays, within each driver. Based on encouraging results of our blood/ saliva validity studies using gas chromatography/tandem mass spectrometry, the proposed research presents a promising opportunity to determine the validity of saliva assays under field conditions with a large sample of injured drivers. The San Diego area is nearly ideal for such a study in terms of its drug problems and the civic energy engaged in addressing them. The site also offers availability of and access to subjects. Given high concordance between saliva and blood assays among these hospitalized drivers, saliva methods can then be used alone to determine drug presence and quantity among an exposure sample from the at-risk population of drivers, using roadside surveys in a second, subsequent field study (Phase 2). The major specific aims of this proposal (Phase 1) consist of determining: (1) differences in prevalence, type, and quantity of drugs and alcohol among the different categories of drivers; (2) relative risk functions for the major drugs and alcohol found among the drivers in Phase 1 versus Phase 2; (3) assessment of driver responsibility regarding relative risk, accident severity, and type and quantity of drugs and alcohol; (4) relation between accident severity and the presence, type, and quantity of drug and/or alcohol; (5) relation between the general effect of the drug found and the type of accident; and (6) utility of models of substance use and abuse for predicting type of consequences of accident, and dangerous driving. Following Phase 2, mid-term objectives (Phase 3) involve developing a prevention/intervention project focused on drugs, drinking, and driving. Long-term objectives include providing the critical information necessary for developing effective public awareness and educational prevention/intervention programs targeting high-risk individuals and groups, as well as high-risk drugs and substance combinations.